Although treatments for depression are effective for many people, not everyone responds to treatment. This lack of treatment response could be due, in part, to the presence of multiple underlying causes of people's depression. This study aims to identify subtypes of depression, based on two factors: how successful people perceive themselves to be at regulating their affect in everyday life; and how much activity in the parasympathetic nervous system increases during moments when people try to regulate. The study involves ambulatory assessment of affect, regulation strategies, and physiological activity in everyday life, in a sample of young adults with remitted major depressive disorder and healthy volunteers. We will study regulation responses in the lab to further determine how subtypes differ in neural, physiological, and behavioral responses. Finally, participants will be randomly assigned to a remote, self-administered biofeedback intervention (vs. control intervention) designed to increase parasympathetic activity and physiological regulation success. While engaging in biofeedback at home for 10 days, participants will simultaneously repeat the ambulatory assessments. This design will allow us to determine the proximal impact of biofeedback on indices of regulation success in everyday life, and whether biofeedback has differential impact on regulation success for different subtypes.

Inclusion Criteria for Participants with Remitted Depression:

1. Age 18-27.
2. Meeting criteria for lifetime major depressive disorder.
3. Currently meeting criteria for full remission (absence of clinically significant symptoms) for at least eight weeks, and having a Hamilton Depression Rating Scale score of less than or equal to 7.

Inclusion Criteria for Healthy Volunteer Participants:

1. Age 18-27.
2. No lifetime history of any psychiatric disorder.
3. No first-degree relatives with a mood disorder.

Exclusion Criteria (same for all participants):

1. Change in psychotropic medication use within the last 30 days
2. Autism spectrum disorder
3. Current eating disorder
4. Intellectual disability
5. Substance use disorder within the past 6 months
6. Contraindications for magnetic resonance imaging or electrocardiogram assessment (e.g., presence of metal in body, claustrophobia, cardiac device, pregnancy).

Per our data sharing plan, we plan to share the de-identified final research data with the broader scientific community via the National Institute of Mental Health Data Archive. This includes fMRI data, ambulatory data, and clinical, behavioral, and self-report measures.